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Discussion Starter #1
My friends 1983 yamaha ss 440, we were driving it around and it was running just fine then it just bogged and you try giving it throttle and it just bogs. And now we cant get it started, do you guys know what could be wrong
 

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just from past experience's here but it sounds an awful lot like crank seals to me. I could be wrong but its were I'd start looking.

Let the sled sit and cool off for a while, then try to start it. If it start's spray a small amount of carb cleaner or starting fluid around the crank behind the clutch and on the other side of the motor. if it rev's up you have a bad crank seal.
 

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It could also be fouled plugs. Pull the old ones out and look at them or just drop new ones in if they look questionable. Plugs aren't that expensive.

I generally think cheap easy fixes first and work my way up. [;)]
 

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Discussion Starter #4
i tryed to get it started and it wont even fire, we sprayed a little of the carba nd choke cleaner in the intake and then it would fire but then die out right away, u guys know anything else.
 

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It's not out of gas is it? I always check the obvious first, you never know.
 

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are you getting spark at all?
 

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Check to see that you fuel pump is working. ie: pulse line still connected and pump is moving fuel when you pull her over.
 

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if you haven't already done so, try changing the fuel filter, then pull the sled over and see if it start's, also you might try cleaning the carbs again, you might have a float stuck not allowing fuel to get to the carbs. However it is sounding more and more like a bad crank seal to me. I went through this on a 78 john deere 440 liquifire a few years back. the only way I could get it to start and run was by dumping fuel into the cylinder's, it would start and run a few second's and die, wouldn't pull any fuel to the carbs. eventually got tired of messing with it and gave it to a buddy of mine. He pulled the motor, put crank seals in it. and it fired on the second pull.
 

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Originally posted by Luke
[br]Check to see that you fuel pump is working. ie: pulse line still connected and pump is moving fuel when you pull her over.
This would also be my next choice. Just pull the gas lines off the carb and crank it over. If fuel shoots out you have eliminated the fuel pump to the tank. Then you get to start cleaning carbs, and this means completely disassemble it and clean the crap out of it.

If that doesn't help, then spray starting fluid around the crank seals and see if they are leaking. As you pull it over bubbles will form if there is a leak.
 

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^^^^^^^^^^^^^^^^^
wouldn't the crank seals be ruled out if the fuel pump is working? if the seals are bad there won't be enough vacuum to the fuel pump for it to pump fuel.
 

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iv had this happen one time, actually twice, for me it was a piston that dropped a skirt, just started bogging like a fouled plug, checked everything and in the end pulled the exhaust off and could see piston dust in there
 

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Originally posted by rev500ss
[br]^^^^^^^^^^^^^^^^^
wouldn't the crank seals be ruled out if the fuel pump is working? if the seals are bad there won't be enough vacuum to the fuel pump for it to pump fuel.
The line from the crankcase to the fuel pump is an impulse line. Part of the time, it's under vacuum (when the piston is going up). Part of the time, it's under pressure (when the piston is going down). Part of the time, it's neutral (at top and bottom of the stroke). The pressure/vacuum cycle causes the diaphram in the fuel pump to move back and forth, and that's what pumps the fuel.

Crank seals would have to be REALLY bad for there to be no pulse to move the diaphram and move fuel.

Like Blackcat said... make sure it's getting fuel from the fuel pump, then through the carbs, then worry about the crank seals. The first two are way cheap; the last one takes a bit more effort and money to fix.
 

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It's been explained to me like this. Think of the fuel pump as a Turkey Baster. You create a vaccum by sqeezing the top and letting go, the juices then fill that void, so the only way to expell the liquid is to squeeze the top by applying pressure.
 

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yeah, I knew it was an impulse, guess I was just going off past experiences when my old JD's crank seals took a crap. acted just like what he was describing, then wouldn't start at all. ended up being the crank seals. you have to have the vacuum to make the pump operate properly, pushing on the diaphram only allows a small amount of fuel into the pump each cycle right. not nearly enough to fill a carb, let alone produce enough vacuum to properly pull the fuel in to the crank case from the carbs. it doesn't take long for bad seals to go completely out. at least they didn't on my old JD. just my .02
 

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The vaccum "sucks" gas from the tank, the pressure pushes the gas to the carbs. I'm guessing that's what you meant...[;)]

What you said makes sense, but really for it to effect the pump that much the seal would have to be pretty bad I would think considering the size of the diaphram. I'm not sure how long it would take to go from a small leak to a large one, but I am sure it has a lot of variables involved.

I guess it's not that hard to check them, not that hard to check the pump either. Whatever a person feels like doing first I guess.

I just like to start with the smaller things first and work my way up.
 

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I had an 82 SS 440 and an 81 Exciter that use to do the same thing. All I did was pull and clean the carb. The pilot jets on both sleds were clogged. Also clean the bowl and all other jets. It normally bogged a little till I opened it up on the trail for the first minute or two then was fine the rest of the day.
 
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